Why Is AVS Needed Instead of CT for Primary Aldosteronism?

A CT scan can show what your adrenal glands look like, but it cannot always tell you which gland is actually producing too much aldosterone. An adrenal nodule found on a CT scan is often an incidentaloma—a mass found unexpectedly. While many of these are benign (harmless) and non-functioning lumps, some can produce hormones, and others require evaluation to rule out other issues. The true source of your excess aldosterone might be tiny, invisible cells in the opposite gland or even in both glands.

For most patients considering surgery for primary aldosteronism, medical guidelines generally recommend adrenal vein sampling (AVS) ^[1]. AVS helps determine whether the excess hormone is coming predominantly from one gland or both, guiding your medical team to the most appropriate treatment. (In some specific cases—such as younger patients with very clear clinical signs, low potassium, and a distinct unilateral nodule—a doctor might consider surgery without AVS, but this is an exception to the rule ^[2]).

The Limits of a CT Scan

A CT scan is excellent at mapping out the anatomy of your adrenal glands, and it remains useful for identifying concerning masses. However, it only shows structure, not function. Finding a lump does not guarantee it is the source of your primary aldosteronism.

Studies show that imaging alone can sometimes be misleading:

• Non-functioning nodules: You can have a visible lump on one gland that doesn’t produce hormones, while the other gland is actually causing the problem. In one study of patients who had excess aldosterone coming from both glands, some individuals had a visible nodule on their CT scan that turned out to be completely unrelated to their hormone excess ^[3].
• Invisible sources: A normal-appearing gland on a CT scan doesn’t guarantee it is healthy. Microscopic cells that overproduce aldosterone can be easily missed by imaging. Research has found that excess aldosterone is sometimes produced by glands that look completely normal on a scan ^[4].
• Frequent disagreements: When comparing CT scans against AVS results, large studies have found that imaging incorrectly identifies the source of the problem in up to a third of cases ^{[5] [6]}.

Because of these limitations, relying only on a CT scan can sometimes lead to ineffective surgery, where the removed gland was not the main source of the problem.

What is AVS and What Are the Risks?

Adrenal vein sampling (AVS) is an invasive procedure usually performed by an interventional radiologist. It involves using local anesthetic and threading a tiny catheter (tube) through a vein in your groin or arm. The radiologist uses contrast dye to help guide the catheter and collects blood directly from each adrenal vein, as well as a peripheral vein.

The procedure allows your medical team to estimate the relative secretion of aldosterone from each side. While it provides vital information, AVS has practical limitations and risks:

• Success rates: The procedure can sometimes be technically unsuccessful or provide inconclusive results, often depending on the medical center’s experience ^[7].
• Risks: As an invasive procedure, risks include bleeding, bruising, contrast reactions, or, in rare cases, injury to the adrenal vein ^[8].
• Preparation: Your medical team will give you specific instructions about your medications leading up to the test. Do not stop or change blood pressure, potassium, or aldosterone-blocking medicines on your own, as this can be dangerous and cause severe spikes in blood pressure or drops in potassium. Always follow your center’s specific preparation plan ^[9].

What the AVS Result Can Mean

AVS helps guide your treatment, but it does not guarantee a perfect outcome. Treatment decisions also depend on your overall health, kidney function, potassium levels, and personal preferences.

• Predominantly One-Sided (Unilateral): If one gland is producing the excess hormone, you may discuss surgical removal of that gland (adrenalectomy). Studies associate AVS-guided surgery with higher rates of “biochemical success”—meaning your hormone and potassium levels improve or return to normal—compared to CT-guided surgery ^[10]. However, surgery does not guarantee your blood pressure will completely normalize, and you may still need some blood pressure medication afterward.
• Both Sides (Bilateral): If both glands are overproducing aldosterone, surgery is usually not appropriate. This is not a failure; it is commonly and effectively managed with long-term medication, such as mineralocorticoid-receptor blockers (like spironolactone or eplerenone). These medications control the aldosterone excess, lower blood pressure, and protect your heart and kidneys.
• Inconclusive: If the blood sample was inadequate or unclear, you and your doctor will discuss next steps, which might include repeat testing or moving forward with medical management.